i remember reading once that air that passes under a car with a smooth base has less resistance so helps to beat drag making the car quicker....as opposed to a non enclosed under chassis of a car which has many bits causing drag...

has anyone completely under trayed their car???

My understanding is you're starting to look at ground effects. To be truely effective the car needs to be running a lot lower to the ground.

If you do want to do this (it helps keep muck out of the car) you've also got to bear in mind hot air from the radiator flows out of the bottom of the car - where is it going to go?

Also, how high is your engine now? How high will it be if you have a flat floor and what have you just done to the centre of gravity lifting the engine?

Assuming you're thinking of doing it on a 7-type car, then I'd say it's worth spending your time and energy elsewhere if you want it to go quicker.

People forget that there's air under the car too. A smooth underbody will reduce drag. The centre bit of a seven is smoother than a standard car to start with. You could panel some of the engine bay and round the rear suspension. Be ware that air going into the bay from the nose cone has to escape from somewhere. If you panel in the bottom of the engine bay, you'll need to vent the air somewhere else.

As above, reducing your drag is alway going to be a bonus, but needs to be designed into the car holistically rather than as an afterthought, the benefits of reduced drag will be more than countered by the higher centre of gravity, reduced cooling and posibly even the weight of full flooring. That said a well designed rear diffuser will be a good middle ground.

Personally though as far as aerodynamics go, the best thing to create is downforce, if you look at the high spped runs for 7 type cars 160ish is pretty much the limit before the front end lifts up, more downforce, better traction, better acceleration, better top speed!

A fully flat undertray on your seven can do two things:

Reduce drag, there is a lot of turbulence on the standard model with air flowing through the tunnel, boot cavity, then merging back into the air stream, providing a smooth path will eliminate some of the turbulence.

Secondly, it can provide additional downforce, if you can speed up the air travelling under the car (similar to that of a wing.) then its pressure decreases, the result is downforce.

Now, you have to ask yourself is it worth doing this, the floor is not the least aerodynamic part of the seven, there are benefits to be had elsewhere. In order to increase the downforce your going to need to go pretty fast, and have a car that is pretty low to the ground, so again is this going to give you a noticable improvement?

I opted for a fully flat floor int he Fury, and am fitting one to the seven as part of its winter upgrades, there are few other reasons for this, - it should help keep the road dirt/spray/crud out of the inside of the car, after morocco i'm still pulling half the sahara out of every nook and cranny.

BTW, if anybody is interested, I've forked OpenFOAM to fix a few bugs in simpleFOAM and the various examples, and have started writing a meshing tool to import direct from solidworks without the palaver of using snappy and blockmesh.

Its progressing slowly as I have other things I need to work on at the moment (Like finishing the car) but if your interested let me know and I"ll keep you posted once I make some more progress.

my side pannels are designed to vent the warm air from under the bonnet...also my sump seems to be level with the bottom of the car so for me to make the under trays is a very simple job, and will cost me nowt......

I've bought the ali to do it but never got round to it for the reasons mentioned above (ie what's the point).

If I wanted to go quicker though I'd look at more power or losing weight from the car, trying to make a 7 aerodynamic is like trying to polish the proverbial.

Sevens are not (and never will) be aerodynamic...

IMHO anyway...

Just remember OIL CHANGES

quote:

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Originally posted by BenB

Sevens are not (and never will) be aerodynamic...

IMHO anyway...

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Here's mine;



Vortx Undertray

And this is the chassis with the undertray mounting brackets fitted


Chassis & undertray brackets

The tray is made of 2mm ally (the thinner stuff is too flimsy) and is mounted to the brackets using ally button head bolts and rubber well-nuts

I'll be fitting large carbon louvres to the bonnet to ensure air flow through the rad and engine bay. I'm also going to add carbon NACA ducts for the cold air feed to the airbox.

[Edited on 25/2/10 by sucksqueezebangblow]